Syringe guard with selected needle configurations

ABSTRACT

A device for expelling a fluid through a needle mounted on a hub includes an elongated luer member that has a distal portion dimensioned to engage the needle hub to provide fluid communication between the luer member and the needle. An adapter anchors the luer member within the device. Slidingly mounted on the adapter is a cylindrical-shaped inverted plunger that is movable thereon between an advanced position and a withdrawn position. A needle guard is biased by a biasing member to extend distally from the luer member when the plunger is in the advanced position. The guard is selectively engageable with the plunger to be retracted to expose the distal portion of the luer member for fluid engagement with the needle hub when the plunger is moved to the withdrawn position.

This application is a continuation of U.S. Nonprovisional applicationSer. No. 11/055,415, filed on Feb. 10, 2005, which is acontinuation-in-part of U.S. Nonprovisional application Ser. No.10/983,108, filed on Nov. 5, 2004. The contents of application Ser. Nos.11/05,415 and 10/983,108 are herein incorporated by reference in theirentirety.

FIELD OF THE INVENTION

The present invention pertains generally to devices for providinginjections with needles. More particularly, the present inventionpertains to protective devices for receiving needles prior to theadministration of an injection. The present invention is particularly,but not exclusively, useful for passively covering and protecting theneedle of an injection syringe after its use.

BACKGROUND OF THE INVENTION

Recent research from the Centers for Disease Control and Prevention(CDC) shows that approximately 384,000 needle sticks or similar injuriesoccur among health care workers in U.S. hospitals each year.Unfortunately, each accidental needle stick has the potential to exposea health care worker to a life-threatening virus such as hepatitis orHIV. In addition to the needle sticks that occur in hospitals,accidental needle sticks can also occur in other health care settings.For example, needle stick injuries can occur at clinics or during homehealth care. In fact, some studies have estimated that over 600,000needle sticks occur in the U.S. each year, and approximately 1,000 ofthese accidental needle sticks result in a life-threatening Infection.

For each accidental needle stick, health care providers are obligated totest and counsel the exposed worker. Further, follow-up testing for HIVmust be conducted approximately six months after the exposure. It is tobe appreciated that the costs associated with the testing, lab work, theworker's lost time, and the associated tracking and administrativecosts, can be considerable.

Accidental needle sticks can occur in several ways. For example, suddenmovement by the patient can cause a health care worker to lose controlof a syringe, resulting in injury. Attempts to manually recap a needlefollowing an injection can also result in injury. Moreover, injuriesoften result when contaminated, unprotected needles are left unattendedor disposed of improperly. In addition to accidental needle sticks,unnecessary exposure to bloodborne pathogens can result when a healthcare worker mistakenly reuses a contaminated needle on a patient.

One particular type of syringe that is prone to needle stick injuries isthe fillable injection syringe. In overview, these fillable injectionsyringes are designed to be filled with a medicament from a medicamentvial by the same user that administers an injection. Heretofore, atypical procedure has involved removing a cap that covers the sharpneedle tip of the fillable injection syringe. With the needle exposed,the needle tip is inserted into a vial containing medicament. This stepgenerally occurs just prior to an injection. Next, the plunger isdepressed to void the syringe chamber of air. With the syringe voided,the plunger is retracted to draw a specified quantity of medicament intothe syringe chamber. Once the medicament has been loaded into thesyringe, the needle is then inserted into a patient and the plunger isdepressed to inject the medicament into the patient. After theinjection, the needle is removed from the patient and often must bemanually recapped to protect the contaminated needle. After recapping,it is often difficult to distinguish between used and unused syringes.

Fillable injection syringes and needles are often obtained separately.Typically, the syringes are available for use with different sizedneedles. This allows doctors to obtain and store fewer syringes. Then,when an injection is needed, a desired needle is simply mounted on asyringe.

In light of the above, it is an object of the present invention toprovide a device that passively covers and protects a needle after firstfilling the device with medicament and then injecting the medicamentinto a patient. It is another object of the present invention to providea device which guards the needle prior to an injection procedure anduses the same guard to passively guard the needle after an injectionprocedure. It is still another object of the present invention toprovide a device in which the position of the needle guard is controlledand regulated by plunger movements that are required in a typical filland inject procedure. It is yet another object of the present inventionto provide a device having an integral mechanism that prevents reuse ofthe syringe (after use and contamination) by disabling the plunger atthe completion of an injection procedure. Still another object of thepresent invention is to provide such a device for use with commerciallyavailable needles. Still another object of the invention is to provide adevice with a needle guard that is movable to allow mounting of a needleon the device before use. Yet another object of the present invention isto provide a protective device for a medical syringe that is easy touse, relatively simple to implement, and comparatively cost effective.

SUMMARY OF THE INVENTION

A device for expelling a fluid, such as a medicament, through ahypodermic needle mounted on a hub includes an extended luer member thathas a proximal portion, a distal portion and a fluid conduit extendingalong an axis therebetween. The distal portion of the extended luermember is dimensioned to engage the needle hub to provide fluidcommunication between the fluid conduit and the needle. When engaged,the needle extends away from the distal portion of the luer member to asharp needle tip at its own distal end. Additionally, the deviceincludes an adapter for anchoring the proximal portion of the luermember. The adapter includes a substantially cylindrical-shaped wallsurrounding a cavity bounded by an open distal end and a proximal endsubstantially covered by a base. Slidingly mounted on the adapter is acylindrical-shaped inverted plunger that is movable thereon between anadvanced position and a withdrawn position. When the plunger is in thewithdrawn position, a fluid chamber is created between the plunger andthe adapter base. Specifically, the chamber is formed by a seal engagingthe proximal portion of the luer member which is slidingly received bythe plunger to form a fluid tight boundary for the fluid chamber. Forthe present invention, a tube-shaped needle guard having a lumen isbiased by a biasing member such as a spring to extend distally from thedistal portion of the luer member when the plunger is in the advancedposition. The guard is selectively engageable with the plunger to beretracted into the adapter cavity and over the elongated luer member toexpose the distal portion of the luer member for fluid engagement withthe needle hub when the plunger is moved to the withdrawn position.

In greater structural detail, the luer member includes a head sectionthat engages the adapter. The head section is connected to a shaftsection which extends distally from the head section along the axis to ashaft end that is spaced from the head section by a shaft length that isat least as long as the length of the adapter. Therefore, the luermember extends through the cavity and the open distal end of theadapter. As the extremity of the distal portion of the luer member, theshaft end is dimensioned for engagement with the needle hub. Engagementbetween the needle hub and shaft end may be achieved through a number ofknown methods. For instance, the needle hub may include acircumferential protrusion that fits into a corresponding circulargroove on the shaft end. Alternatively, the needle hub may include maleor female threadings to allow the hub to be screwed into reciprocalthreadings on the shaft end. Or, more simply, the needle hub may beslipped snugly onto the shaft end.

As described in greater detail below, a mechanism provides selectiveengagement between the plunger and guard during the course of aninjection procedure. More specifically, the plunger movements that arerequired to expose the distal portion of the extended luer member formounting a needle thereon, to fill the fluid chamber, and to dispense afluid from the fluid chamber also function to control the position ofthe guard. In functional overview, prior to an injection procedure, theguard is locked in an extended position distal of the luer member andcan only be unlocked by a movement of the plunger. Once unlocked, theguard can be retracted to expose the distal portion of the luer member.This allows the needle hub to be mounted on the distal portion of theluer member, and in addition, allows the needle to be inserted into amedicament vial to fill the fluid chamber and to be inserted into apatient for an injection. When the plunger is withdrawn proximallyrelative to the adapter to create the fluid chamber, the plunger andguard engage one another, and the guard moves proximally to expose thedistal portion of the luer member and a needle mounted thereon. On theother hand, when the plunger is advanced (i.e. moved distally), theplunger releases the guard. Once released, the guard is free to movedistally under the influence of the spring. As a consequence of thisinteraction, after the plunger is depressed to complete an injection,the guard is released and allowed to move distally to its extendedposition to cover and protect the needle.

In operation, the plunger is initially located in an advanced positionrelative to the adapter. Next, the plunger is withdrawn proximally whichcauses the plunger to engage the guard and to move the guard proximallywith the plunger to a retracted position. With the guard retracted, thenext step is to mount the needle hub onto the exposed shaft end of theluer member. Then the distal tip of the needle may be inserted into amedicament vial. At this point, the plunger can be depressed to expelair into the vial and void the fluid chamber. During plungeradvancement, the plunger operatively disengages the guard. Thus, distalmovement of the guard is only prevented by the contact between the guardand the vial. Next, the plunger can be withdrawn to fill the fluidchamber with medicament. During this plunger withdrawal, the plungeragain engages and retracts the guard. Thus, when the needle is removedfrom the vial, the distal tip of the needle remains unguarded andexposed. The syringe is now ready for an injection.

To inject a medicament into a patient, the distal tip of the needle isinserted into the patient and the plunger depressed. This distaladvancement of the plunger releases the guard. Once released, the guardis free to move distally under the influence of the spring. Thus, as theneedle is withdrawn from the patient, the needle retracts proximallyinto the guard, which remains in contact with the patient's skin. Oncethe syringe has been removed from the patient, the plunger and adaptercan be advanced distally relative to the syringe body to lock the guardin place.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of this invention, as well as the invention itself,both as to its structure and its operation, will be best understood fromthe accompanying drawings, taken in conjunction with the accompanyingdescription, in which similar reference characters refer to similarparts, and in which:

FIG. 1 is a perspective view of a device for expelling a fluid through ahypodermic needle mounted on a hub, shown in its initial configuration;

FIG. 2 is a perspective view of a hypodermic needle mounted on a hub foruse with the device of FIG. 1;

FIG. 3A is a sectional view of the syringe as seen along line 3-3 inFIG. 1, shown after a needle has been mounted on the luer member andwith the guard locked over the needle's distal tip;

FIG. 3B is a sectional view of the syringe as in FIG. 3A, shown after aplunger movement has unlocked and distally retracted the guard;

FIG. 3C is a sectional view of the syringe as in FIG. 3A, shown afterthe needle's distal tip has been inserted into an object (i.e.medicament vial or patient) and thereafter the plunger has been advancedproximally;

FIG. 3D is a sectional view of the syringe as in FIG. 3A, shown afterthe plunger and adapter have been advanced distally relative to thesyringe body to lock the guard in position and prevent inadvertent reuseof the syringe;

FIG. 4A is a sectional view of the syringe as seen along line 4-4 inFIG. 1, shown after a needle has been mounted on the luer member andwith the guard locked over the needle's distal tip;

FIG. 4B is a sectional view of the syringe as in FIG. 3A, shown after aplunger movement has unlocked and distally retracted the guard;

FIG. 4C is a sectional view of the syringe as in FIG. 3A, shown afterthe needle's distal tip has been Inserted into an object (i.e.medicament vial or patient) and thereafter the plunger has been advancedproximally; and

FIG. 4D is a sectional view of the syringe as in FIG. 3A, shown afterthe plunger and adapter have been advanced distally relative to thesyringe body to lock the guard in position and prevent inadvertent reuseof the syringe.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring initially to FIG. 1, a syringe device for expelling a fluidthrough a needle mounted on a hub is shown and generally designated 10.As shown in FIG. 1, the device 10 includes a substantially cylindricalsyringe body 12 that is centered on an axis 14 and formed with a fingergrip 16 at its proximal end. FIG. 1 further shows that the device 10includes an adapter 18 sized to fit within the syringe body 12. Theadapter 18 includes a cylindrical portion that is also centered on theaxis 14. For the device 10, a substantially cylindrical needle guard 20is provided and positioned co-axially with both the syringe body 12 andadapter 18. The guard 20 is sized to fit within the adapter 18. It canbe further seen that the device 10 includes a plunger 22 that is formedwith a grip flange 24 at its proximal end.

Referring to FIG. 2, a straight, elongated hypodermic needle 26 is shownextending from a sharp needle tip 28 to a needle hub 30. As best seen inFIG. 3A, the needle 26 may be mounted to the passively guarded, fillableinjection device 10. Specifically, the device 10 includes a luer member32 that receives and engages the needle hub 30. The luer member 32 has aproximal portion or head 34. Extending distally from the head 34 is asubstantially cylindrical shaft 36 centered on the axis 14. The needlehub 30 is mounted to the luer member 32 at the shaft's distal portion ordistal shaft end 38. Additionally, the head 34 has a proximal side 33and a distal side 35 that engages the adapter 18.Circumferentially-spaced truss-like webs 40 are provided on the luermember 32 to reinforce the connection between the shaft 36 and the head34. Furthermore, the luer member 32 includes a pipe-like conduit 39 thatextends from the proximal side 33 of the head 34 to the shaft end 38.When the needle hub 30 is frictionally mounted on the shaft end 38, theneedle hub 30 and luer member 32 are sealed together to establish fluidcommunication between the needle 26 and the conduit 39.

As shown in FIG. 3A, the adapter 18 engages the luer member 32 about thewebs 40 thereby preventing rotational movement therebetween. The adapter18 includes a substantially cylindrical wall 42 that is centered on theaxis 14 and forms a cavity 43. The wall 42 extends from a proximal end44 substantially covered by a base 45 to an open distal end 46. At itsproximal end 44, the adapter 18 has a narrow circumference and isdesigned to engage the distal side 35 of the head 34 of the luer member32. At its distal end 46, the adapter 18 has a broad circumference andis designed to engage the plunger 22 and receive the guard 20. As can beseen in FIG. 3A, the adapter 18 also includes two oppositely positioned,axially aligned slits 48.

As best seen in FIG. 3A, the adapter 18 is sized to allow thecylindrical guard 20 to move along the axis 14 into and out of theadapter cavity 43. Specifically, the guard 20 may be moved between anextended position 49 (shown in FIGS. 3A and 4A) to a retracted position53 (shown in FIGS. 3B and 4B). Structurally, the guard 20 is a shellforming a lumen 51 that extends between an open proximal end 50 and anopen distal end 52. The guard 20 includes abutments 54 that extendradially outward from the proximal end 50.

Also in FIG. 3A, it can be seen that the inverted plunger 22 has asubstantially cylindrical side member 56 that extends from a closedproximal plate member 58 to an open distal edge 60. Structurally, thecylindrical side member 56 surrounds a fluid chamber 62 and is slidinglymounted on the proximal end 44 of the adapter 18. FIG. 3A further showsthat the plunger 22 is formed with tangs 64 that extend radially inward(i.e. toward the axis 14) and distally from the cylindrical side member56 of the plunger 22.

It can be seen in FIG. 3A, that the device 10 includes an elastomericseal 66 that is attached onto the proximal end 34 of the luer member 32.Specifically, the seal 66 is press fitted onto the proximal end 34 ofthe luer member 32. As shown, the seal 66 has a generally fusiform orspindle-like shape and is formed with a through-hole 68. When the opendistal edge 60 of the plunger 22 is slid over the luer member 32 andadapter 18, the seal 66 compresses between the luer member 32 and thecylindrical side member 56 of the plunger 22 to establish sealed fluidcommunication between the fluid chamber 62 and the conduit 39 of theluer member 32. When the needle hub 30 is mounted on the luer member 32to establish fluid communication between the needle 26 and the conduit39, the plunger 22 can be moved to a withdrawn position 61 (shown inFIGS. 3B and 4B) to draw fluid through the needle 26 and into thechamber 62. Furthermore, the plunger 22 can be moved to an advancedposition 63 (shown in FIGS. 3C and 4C) to expel fluid from the chamber62 through the needle tip 28.

As further shown in FIG. 3A, the syringe body 12 extends from an openproximal end 70 to an open distal end 71. Positioned at the proximal end70, the finger grip 16 includes a recess 72 sized to receive the gripflange 24 of the plunger 22. Functionally, the plunger 22 can beadvanced distally after an injection until the grip flange 24 ispositioned in the recess 72. Once the grip flange 24 is positioned inthe recess 72 it cannot be removed; therefore, subsequent movement ofthe plunger 22 relative to the syringe body 12 is effectively prevented.

Turning to FIG. 4A, other features of the device 10 may be seen.Specifically, the adapter 18 is shown having cam levers 74 positioned atits distal end 46. The cam levers 74 are in a biased position 76 inwhich the plunger 22 forces them to be coincident with the rest of thecylindrical wall 42. However, the cam levers 74 mechanically prefer arelaxed position 78 (shown in FIG. 4B) in which the distal ends 80 ofthe cam lever 74 extend radially outward from the cylindrical wall 42.

As shown in FIG. 4A, the guard 20 has hinges 82. Similar to the camlevers 74 of the adapter 18, the hinges 82 of the guard 20 have arelaxed position 84 in which the proximal ends 86 of the hinges 82extend radially outward from the rest of the guard 20. The biasedposition 88 of the hinges 82 is shown in FIG. 4B.

As further shown in FIG. 4A, the syringe body 12 can also includeflanges 90 at its distal end 71. The flanges 90 extend distally andradially inward from the cylindrical portion 92 of the syringe body 12.Their purpose is discussed below.

By cross-referencing FIGS. 3A-D and 4A-D, it can be seen that the device10 includes a mechanism to lock the guard 20 in an extended position 49covering the needle tip 28 prior to an injection procedure. Once locked,the guard 20 can only be unlocked by movement of the plunger 22. Aspreviously discussed, the adapter 18 is formed with cam levers 74 havingdistal lever ends 80. Comparing FIG. 4A with FIG. 4B, it can be seenthat the cam levers 74 are deflectable by the cylindrical side member 56of the plunger 22 from a relaxed position 78 (FIG. 4B) to a biasedposition 76 (FIG. 4A). In the relaxed position 78 (FIG. 4B), the camlevers 74 extend radially outward from the remaining cylindrical sectionof the adapter 18. On the other hand, as shown in FIG. 3A, in the biased(i.e. deflected) position 76, the cam levers 74 are coincident with theremaining cylindrical wall 42 of the adapter 18. When the plunger 22 isin the advanced position 63 shown in FIG. 4A, the cylindrical sidemember 56 of the plunger 22 contacts the cam levers 74 and deflects theminto the biased position 76. As shown in FIG. 4A, when the cam levers 74are in the biased position 76, the lever ends 80 engage the proximalends 86 of the hinges 82 of the guard 20 and prevents proximal movementof the guard 20. When the plunger 22 is in its withdrawn position 61 asshown in FIGS. 3B and 4B, the cam lever 74 relaxes into its undeflected,outward position 78 (as shown in FIG. 4B) and allows the guard 20 tomove proximally.

As an additional locking mechanism, the syringe body 12 may be movedrelative to the adapter 18 to deflect the cam levers 74 of the adapter18 with its flanges 90. As shown in FIG. 4D, the flanges 90 are movedtoward the adapter 18 when the plunger 22 and adapter 18 are fullypushed into the syringe body 12. As a result, the flanges 90 contact andforce the cam levers 74 of the adapter 18 to the biased position 76 tolock the device 10 to prevent any further proximal movement of theneedle guard 20. This prevents inadvertent reuse of the device 10.

Operation

Initially, the device 10 is provided without a needle 26. To mount aneedle 26 on the device 10, the needle guard 20 is first moved to theretracted position 53 by withdrawing the plunger 22. Then the needle hub30 is frictionally engaged with the shaft end 38 of the luer member 32as can be understood from FIGS. 3B and 4B. After mounting the needle hub30 on the shaft end 38, the needle guard 20 is allowed to move to itsextended position 49 to cover the needle 26 by moving the plunger 22 toits advanced position 63 as shown in FIG. 3A. As further shown in FIG.3A the tangs 64 of the plunger 22 extend through the slits 48 in theadapter 18 to engage the abutments 54 and retract the guard 20 when theplunger 22 is withdrawn.

From FIG. 4A, it can be seen that the cylindrical side member 56 of theplunger 22 holds the cam levers 74 deflected inward to lock the guard 20and prevent proximal movement of the guard 20. As illustrated by FIGS.3A-B and 4A-B, use of the device 10 begins by withdrawing the plunger22. Such proximal movement of the plunger 22 has several effects.Specifically, as shown in FIGS. 4A and 4B, initial proximal movement ofthe plunger 22 allows the cam levers 74 to relax outwardly from the axis14 and unlock the guard 20 for proximal movement. As shown in FIGS. 3Aand 3B, additional proximal movement of the plunger 22 engages the tangs64 with the abutments 54, causing the guard 20 to be retracted with theplunger 22. Also, withdrawal of the plunger 22 draws air (or otherfluid) through the needle 26 and into the fluid chamber 62.

Once the guard 20 has been retracted as shown in FIGS. 3B and 4B, thenext step is to insert the exposed distal needle tip 28 into amedicament vial (illustrated by surface 94 in FIGS. 3C and 4C). At thispoint, the plunger 22 can be depressed as shown in FIGS. 3C and 4C toexpel air into the vial and void the fluid chamber 62. Comparing FIGS.3B and 4B with FIGS. 3C and 4C, it can be seen that during its advancethe plunger 22 disengages the guard 20. Thus, as illustrated by FIGS. 3Cand 4C, after advancing the plunger 22, distal movement of the guard 20is only prevented by the contact between the distal end 52 of the guard20 and the surface 94. Next, the plunger 22 can be withdrawn to fill thechamber 62 with medicament fluid 95 (note FIGS. 3B and 4B arerepresentative of the configuration of the device 10 after the chamber62 is filled with medicament 95). From FIG. 3B, it can be seen thatduring withdrawal of the plunger 22, the tangs 64 reengage the abutments54. The result is that the plunger 22 engages the guard 20 and preventsdistal advancement of the guard 20. As illustrated by FIGS. 3B and 4B,when the needle 26 is removed from the vial, the distal tip 28 of theneedle 26 remains unguarded and exposed. The device 10 is now ready foran injection.

As illustrated by FIGS. 3C and 4C, to inject a medicament into apatient, the distal tip 28 of the needle 26 is inserted into the patient(represented by surface 94) and the plunger 22 is depressed. As shown inFIG. 3C, the distal advancement of the plunger 22 releases the guard 20.Once released, the guard 20 is free to move distally under the influenceof a coil spring 96 that is interposed between the guard 20 and theadapter 18. Thus, as the needle 26 is withdrawn from the patient, theneedle 26 retracts proximally into the guard 20 which remains in contactwith the patient's skin (represented by surface 94). FIGS. 3A and 4A arerepresentative of the device 10 after the needle 26 has been withdrawnfrom the patient and the needle 26 has passively retracted into theguard 20.

Once the device 10 has been removed from the patient, the plunger 22 andthe adapter 18 can be advanced distally relative to the syringe body 12to lock the guard 20 in place (FIG. 4D). FIGS. 3D and 4D also show thatthis places the grip flange 24 of the plunger 22 in the recess 72 formedin the syringe body 12. Functionally, once the device 10 is in theconfiguration shown in FIGS. 3D and 4D, the plunger 22 is disabled andthe guard 20 completely covers the hollow needle 26 to protect the userfrom unwanted needle sticks and prevents inadvertent reuse of the device10.

While the particular devices and methods as herein shown and disclosedin detail are fully capable of obtaining the objects and providing theadvantages herein before stated, it is to be understood that they aremerely illustrative of the presently preferred embodiments of theinvention and that no limitations are intended to the details ofconstruction or design herein shown other than as described in theappended claims.

1. A method for preparing a hypodermic needle to expel a fluidcomprising the steps of: supplying a needle mounted on a hub; providinga device comprising: (a) an adapter having a cylindrical-shaped wallsurrounding a cavity, wherein the adapter defines an axis and has anopen distal end and a proximal end substantially covered by a base; (b)an elongated luer member having a proximal portion and a distal portionwith a fluid conduit extending therebetween, wherein the proximalportion of the luer member is affixed to the adapter base to extend theluer member along the axis and through the adapter cavity to positionthe distal portion of the luer member proximate the distal end of theadapter; (c) a cylindrical-shaped plunger positioned over the adapterand movable thereon between an advanced position and a withdrawnposition to create a fluid chamber between the plunger and the adapterbase when the plunger is in the withdrawn position; (d) a tube-shapedguard having a lumen, wherein the guard is biased to extend distallyfrom the distal portion of the luer member when the plunger is in theadvanced position, and wherein the guard is selectively engagable withthe plunger to be retracted into the adapter cavity and over theelongated luer member to expose the distal portion of the luer memberfor fluid engagement with the needle hub when the plunger is moved tothe withdrawn position to create the fluid chamber and for subsequentlyexpelling the fluid from the fluid chamber, through the luer member andthrough the needle; and (e) a syringe body slidingly mounted on theadapter for relative axial movement thereon; withdrawing the plunger toretract the guard into the adapter cavity and over the elongated luermember to expose the distal portion of the luer member; engaging the hubof the needle with the distal portion of the luer member to establishfluid communication between the fluid chamber of the plunger and theneedle for subsequently expelling the fluid from the fluid chamber andthrough the needle; and moving the plunger and adapter relative to thesyringe body to lock the guard in an extended position to prevent reuseof the needle.
 2. A method for preparing a hypodermic needle to expel afluid comprising the steps of: supplying a needle mounted on a hub;providing a device comprising: (a) an adapter having acylindrical-shaped wall surrounding a cavity, wherein the adapterdefines an axis and has an open distal end and a proximal endsubstantially covered by a base; (b) an elongated luer member having aproximal portion and a distal portion with a fluid conduit extendingtherebetween, wherein the proximal portion of the luer member is affixedto the adapter base to extend the luer member along the axis and throughthe adapter cavity to position the distal portion of the luer memberproximate the distal end of the adapter; (c) a cylindrical-shapedplunger positioned over the adapter and movable thereon between anadvanced position and a withdrawn position to create a fluid chamberbetween the plunger and the adapter base when the plunger is in thewithdrawn position; and (d) a tube-shaped guard having a lumen, whereinthe guard is biased to extend distally from the distal portion of theluer member when the plunger is in the advanced position, and whereinthe guard is selectively engageable with the plunger to be retractedinto the adapter cavity and over the elongated luer member to expose thedistal portion of the luer member for fluid engagement with the needlehub when the plunger is moved to the withdrawn position to create thefluid chamber and for subsequently expelling the fluid from the fluidchamber, through the luer member and through the needle; withdrawing theplunger to retract the guard into the adapter cavity and over theelongated luer member to expose the distal portion of the luer member,wherein the adapter is formed with an axially extending slit, the devicefurther comprising a tang extending radially inward from the plunger andinto the slit to engage the guard and to retract the guard into theadapter cavity and over the elongated luer member to expose the distalportion of the luer member for fluid engagement with the needle hubduring the withdrawing step; and engaging the hub of the needle with thedistal portion of the luer member to establish fluid communicationbetween the fluid chamber of the plunger and the needle for subsequentlyexpelling the fluid from the fluid chamber and through the needle.
 3. Amethod for preparing a hypodermic needle to expel a fluid comprising thesteps of: supplying a needle mounted on a hub; providing a devicecomprising: (a) an adapter having a cylindrical-shaped wall surroundinga cavity, wherein the adapter defines an axis and has an open distal endand a proximal end substantially covered by a base; (b) an elongatedluer member having a proximal portion and a distal portion with a fluidconduit extending therebetween, wherein the proximal portion of the luermember is affixed to the adapter base to extend the luer member alongthe axis and through the adapter cavity to position the distal portionof the luer member proximate the distal end of the adapter; (c) acylindrical-shaped plunger positioned over the adapter and movablethereon between an advanced position and a withdrawn position to createa fluid chamber between the plunger and the adapter base when theplunger is in the withdrawn position; and (d) a tube-shaped guard havinga lumen, wherein the guard is biased to extend distally from the distalportion of the luer member when the plunger is in the advanced position,and wherein the guard is selectively engageable with the plunger to beretracted into the adapter cavity and over the elongated luer member toexpose the distal portion of the luer member for fluid engagement withthe needle hub when the plunger is moved to the withdrawn position tocreate the fluid chamber and for subsequently expelling the fluid fromthe fluid chamber, through the luer member and through the needle;withdrawing the plunger to retract the guard into the adapter cavity andover the elongated luer member to expose the distal portion of the luermember, wherein the adapter is formed with a cam lever selectivelyengaging the guard to prevent unintended retraction of the guard, andwherein the withdrawing step causes the cam lever to disengage the guardto allow retraction of the guard; and engaging the hub of the needlewith the distal portion of the luer member to establish fluidcommunication between the fluid chamber of the plunger and the needlefor subsequently expelling the fluid from the fluid chamber and throughthe needle.
 4. The method of claim 1, further comprising: advancing theplunger to void the fluid chamber; placing the needle in the fluid;drawing back the plunger to load the fluid chamber with the fluid, thedrawing back the plunger causing the needle guard to be retracted toexpose the needle; inserting the needle into a patient; depressing theplunger to inject the fluid from the fluid chamber through the needleand into the patient and to release the guard from the plunger; andremoving the needle from the patient to allow the guard to slidedistally to cover and protect the needle.
 5. The method of claim 1,further comprising: preventing relative rotational movement between theadapter and the elongated luer member.
 6. The method of claim 1, furthercomprising: establishing sealed fluid communication between the fluidchamber and the fluid conduit of the elongated luer member.
 7. Themethod of claim 1, further comprising: disabling the plunger when theguard is locked in the extended position.
 8. The method of claim 1,further comprising: interposing a coil spring between the guard and theadapter to bias the guard distally.
 9. The method of claim 2, furthercomprising: advancing the plunger to void the fluid chamber; placing theneedle in the fluid; drawing back the plunger to load the fluid chamberwith the fluid, the drawing back the plunger causing the needle guard tobe retracted to expose the needle; inserting the needle into a patient;depressing the plunger to inject the fluid from the fluid chamberthrough the needle and into the patient and to release the guard fromthe plunger; and removing the needle from the patient to allow the guardto slide distally to cover and protect the needle.
 10. The method ofclaim 2, further comprising: preventing relative rotational movementbetween the adapter and the elongated luer member.
 11. The method ofclaim 2, further comprising: establishing sealed fluid communicationbetween the fluid chamber and the fluid conduit of the elongated luermember.
 12. The method of claim 2, further comprising: locking the guardin an extended position to prevent reuse of the needle.
 13. The methodof claim 12, further comprising: disabling the plunger when the guard islocked in the extended position.
 14. The method of claim 3, furthercomprising: advancing the plunger to void the fluid chamber; placing theneedle in the fluid; drawing back the plunger to load the fluid chamberwith the fluid, the drawing back the plunger causing the needle guard tobe retracted to expose the needle; inserting the needle into a patient;depressing the plunger to inject the fluid from the fluid chamberthrough the needle and into the patient and to release the guard fromthe plunger; and removing the needle from the patient to allow the guardto slide distally to cover and protect the needle.
 15. The method ofclaim 3, further comprising: preventing relative rotational movementbetween the adapter and the elongated luer member.
 16. The method ofclaim 3, further comprising: establishing sealed fluid communicationbetween the fluid chamber and the fluid conduit of the elongated luermember.
 17. The method of claim 3, further comprising: locking the guardin an extended position to prevent reuse of the needle.
 18. The methodof claim 17, further comprising: disabling the plunger when the guide islocked in the extended position.
 19. The method of claim 3, wherein thecam lever is movable from a relaxed position wherein a distal end of thecam lever extends radially outward from the cylindrical-shaped wall ofthe adapter to a biased position wherein the distal end of the cam leveris coincident with the cylindrical-shaped wall when the plunger is movedto the advanced position.
 20. The method of claim 19, wherein: the guardcomprises a hinge movable between a relaxed position and a biasedposition; and the cam lever in the biased position engages the hinge inthe relaxed position to prevent proximal movement of the guard.